JDK-8352891 Performance improvements to ByteArrayOutputStream

[Archie Cobbs]

On Fri, Apr 11, 2025 at 8:11 AM Engebretson, John <jengebr at amazon.com>
wrote:

> It seems like a good general-purpose list but I wouldn’t recommend it as a
> direct replacement for either ArrayList or LinkedList; in the former case
> the risk is slower random accesses, and in the latter the risk is to head
> modifications.
>

Interesting results. However I don't think comparing this to both ArrayList
and LinkedList is really fair. Developers choose an implementation based on
how they know they are going to use it: If they are just adding stuff, they
choose ArrayList. If they know they need to insert/remove in the middle,
they choose LinkedList. If they need to add/remove from both ends, they
choose ArrayDeque. Etc.

So the optimal design changes depending on which "flavor" of list usage the
developer is implying when they choose some implementation class.

E.g., if you wanted to target the "ArrayList flavor', then you'd use fixed
size, power-of-two segments. Then get() remains constant time, and insert
and remove remain as painfully slow as ever, but the common "list builder"
usage pattern of "append, append, append, ..., use read-only thereafter"
gets a lot faster.

OTOH variable-sized chunks makes lots of sense for the "LinkedList" flavor.
In fact you could have a LinkedList<T> that just uses an
ArrayList<ArrayDeque<T>> internally :)

-Archie

-- 
Archie L. Cobbs
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